The present invention relates to a rear dump truck with a sieving device which is designed so that when particulate matter including dust and fine particles are loaded, transported and unloaded, upon the unloading the box is tilted up so that the dust and fine particles included in the loaded matter are sifted out and discharged through separate dump doors.
Generally, particulate matter such as ferroalloys, e.g., silicon manganese, ferro silicon and ferrochrome alloys, coke and coal mostly includes homogeneous particulate dust and fine particles from the start of their production. When such material is supplied as a commercial product to a user or as a raw material to another plant, the material is delivered after removing the particulate dust and fine particles through a sieving operation. In the past, it has been the usual practice to effect the sieving of the material delivered by a dump truck by a separate sieving machine installed as a stationary equipment. However, this gives rise to a disadvantage of the sieving operation requiring not only a site and equipment but also a considerable labor and there are another problems of environmental contamination due to the scattering of the particulate dust, etc.
In view of these circumstances, the inventor has already proposed a rear dump truck with a sieving means which eliminates the sieving operation and is capable of effecting the sieving during the discharging of the material or the final stage of the transportation of the material by the dump truck. The details of this dump truck are disclosed in Japanese Laid-Open Patent Application Publication No. 56-28025 published on Mar. 19, 1981 or its issued patent, i.e., Japanese Patent Publication No. 58-58245 (Published on Dec. 24, 1983). The disclosed rear dump truck is so designed that any particulate material requiring sieving can be carried and both the sieving and the discharging of the material can be effected simultaneously by tilting up the box upon the dumping. Also, in case of particulate material containing a large quantity of finely divided particles, there is no danger of the sieved particulate material from being mixed with the minus sieve or undersize fine particles when the box is tilted up. Then, in the case of particulate material of such properties tending to cause solidification of the material, from the standpoint of simplication of the box tilting operation effected by the driver himself and ensuring excellent sieving result at all times, it is absolutely necessary in many cases that during the dumping the tilting up of the box does not cause the particulate material to slide down altogether but allows suitably restrained down flow of the material while stirring the top and bottom layers thereof thus ensuring the uniform sieving of the material. While the rear dump truck disclosed in the publications is provided with the necessary means for this purpose, the means merely comprises a plurality of ridges fixedly arranged on the box floor in the width direction thereof and therefore the means is not sufficient for preventing the occurrence of an avalanche phenomenon of the particulate material due to the tilting up of the box upon the dumping, thus imposing on the operator a complicated task of suitably adjusting the tilting speed of the box, for example.